The present invention relates to a semiconductor device and a method for fabricating the same, more specifically, a semiconductor device including a gate electrode of metal silicide and a method for fabricating the semiconductor device.
In order to improve the characteristics of MISFET devices, techniques of forming the gate electrode of only metal silicide are proposed. The gate electrode formed of metal silicide alone can decrease the gate resistance in comparison to a gate electrode of the polycide structure and can also suppress the depletion of the gate electrode.
As a technique of forming the gate electrode of only metal silicide, it has been proposed that a dummy electrode of amorphous silicon or polycrystalline silicon is formed at the part where the gate electrode is to be formed, a metal is deposited, and thermal processing for the silicidation reaction is made to substitute the dummy electrode into the metal silicide. This technique retains the consistency with the conventional process of forming the source/drain regions by self-alignment with the gate electrode while keeping off the contamination, etc. of the silicon substrate with the metal material.
Otherwise, it is known that tensile strains exerted to the silicon crystal improve the mobility of the electrons in the crystals, and semiconductor device structures utilizing this feature are proposed. A known example of these structures is a film for applying stress called a stressor film which is formed to cover the gate electrode. As the stressor film, silicon nitride-based insulating films, such as silicon nitride film, silicon oxynitride film, etc., are predominantly used. A stressor film having tensile stress is formed over the gate electrode from the side wall thereof onto the upper surface thereof, whereby the tensile strain is applied to the channel region, and the mobility of the electrons in the channel region is improved. Thus, the MIS transistor can be operated at high speed.
However, the present inventors discovered that when a gate electrode of metal silicide is formed by the above-described technique, it is difficult to induce lattice strain into the channel region by the use of a stressor film.
In the technique of replacing the dummy electrode by metal silicide, an inter-layer insulating film is formed, covering the dummy electrode, the surface of the inter-layer insulating film is planarized to expose an upper surface of the dummy electrode by the CMP (Chemical Mechanical Polishing) method or others, then a metal film is deposited, and thermal processing for silicidizing the metal film is made to thereby substitute the dummy electrode into the metal silicide.
Accordingly, even when the stressor film is formed over the dummy electrode from the side wall onto the upper surface, the stressor film on the upper surface of the dummy electrode is removed in the step of planarizing the inter-layer insulating film, and the tensile stress cannot be applied to the channel region.